1. Field of the Invention
The present invention relates to three-dimensional printing systems.
2. Description of the Related Art
A three-dimensional printing apparatus known in the art exposes a liquid photo-curable resin stored in a tank to light so as to cure the photo-curable resin, thus printing a three-dimensional object.
A three-dimensional printing apparatus of this type includes a base provided with an opening, a tank placed on the base, and a raisable and lowerable holder disposed over the tank. An optical system is disposed under the tank. For example, the optical system includes a light source that emits light and a mirror. A portion of a photo-curable resin stored in the tank is exposed to the light emitted from the light source, and this portion of the photo-curable resin is cured. By controlling a position at which the resin is to be exposed to the light, a position at which the resin is to be cured changes to a suitable position, and the cured resin can thus form a desired cross-sectional shape. Such desired cross-sectional shapes are continuously formed downward by sequentially raising the holder. As a result, a desired three-dimensional object is printed.
A deficiency of a resin in the tank in printing a three-dimensional object makes it impossible to complete or finish printing a desirable three-dimensional object. To avoid such a situation, a photo-curable resin is abundantly stored in the tank in advance in the three-dimensional printing apparatus known in the art. This may cause a large amount of the resin to remain in the tank after printing of a three-dimensional object has been completed (i.e., after the printing of the three dimensional object is completely finished). The remaining resin is used again to print a next three-dimensional object. Unfortunately, a portion of this remaining resin may have been exposed to the light from the light source during printing of the previous three-dimensional object, thus degrading the photo-curable resin. The use of the degraded photo-curable resin in the next printing of a three-dimensional object fails to form a desirable cross-sectional shape, resulting in a low quality three-dimensional object.